Aeration accelerates the breakdown of biological pollutants and is a key factor in returning the water to a healthy organic state.

Sand filters are commonly used to provide high-quality "polishing" of wastewater, which is often necessary if the water is to be re-used without being returned to nature. Most lay people are unaware that nature's most powerful cleansing tool for water is actually the ground itself; as water trickles down through soil, sand, and rock on its way to aquifers hundreds of feet below the surface, it is cleaned in an incredibly effective way. Sand filters can be used to surrogate this cleansing action.

Chlorination has long been the most widely-used method of water disinfection.

Particle sensors are especially important in closed-loop water recycling systems, since they provide rapid detection of hazards like Cryptosporidium and Giardia.

Ultraviolet (UV) filters are a thorough and modern way to disinfect water. UV radiation is already used in medicine to disinfect and sterilize hospital instruments, among other things, and the effectiveness of UV disinfection of water is also known to be effective.